Among the conventional photovoltaic systems, the concentrating photovoltaic (CPV) could focus the sun light on the solar cells through optical devices so as to decrease the area of the solar cells and lower the cost of power generation. However, the concentrating photovoltaic is very sensitive to the incident angle of the sunlight. In order to focus the sun light on the solar cells correctly, the sun-tracker is used to adjust the light axis of the light-concentrating module facing sun directly. Whereas, the area of the high-concentration photovoltaic (the light concentration ratio is more than 500-fold) is further decreased, so the light-concentrating module has little tolerance to the angle deviation of the sun-tracker, and the accuracy of the sun-tracker is getting more and more important.
In the concentrating photovoltaic systems, usually pluralities of sensors are needed to cooperate with the sun-tracker. The sensors could be classified into two categories by their view angle: one is the wide view angle type and the other is the narrow view angle type. Because each sensor is disposed at different positions, the wide view angle type of sensors could generate different voltage output corresponding to the non-uniform light sensed by the sensors, and the direction of the strongest sunlight could be determined according to the voltage values. The main application of the wide view angle type of sensors is active tracking. The advantages of the wide view angle type of sensors are wide view angle, and the strongest sunlight still could be determined even when the weather is bad or sun is sheltered by clouds. However, the disadvantage of the wide view angle type of sensors is low accuracy, and the angle deviation from the strongest light, thus could not be projected or calculated. On the other hands, the narrow view angle type of sensors could accurately project or calculate the angle deviation of the sunlight by using the optical properties and the space geometry relationship, and the main applications of the narrow view angle type of sensors are recording the sunlight deviation angle, or correcting the initial assembling errors during the sun trajectory tracking. However, the disadvantages of the narrow view angle type of sensors are small view angle and the low accuracy when the weather is bad or the sun is sheltered by clouds.
In summary, the function of the conventional sensors is relatively simple, and common photovoltaic systems usually need different kinds of light sensors when operate different sun-tracking. Besides, different kinds of situation needs different kinds of sensors to deal with, for example, the wide view angle type of sensors could be operated under bad weather or cloudy situation, but the accuracy is too low and the angle deviation from the strongest sunlight could not be determined. At this time, if we want to determine the tracking performance, we need to accumulate the tracking data for a long time or install extra sensors with higher accuracy, and this causes the inconvenience and cost up when use the photovoltaic systems to generate electric power.